JPH0214291B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a method of easily and easily producing U ₃ O ₈ powder with a crystal size of 40 to 90 μm by igniting a finely powdered uranium compound with an oxidation number of +4 to +6 at normal pressure in an oxygen-containing atmosphere. Concerning an economical method of manufacturing.

Research is underway to convert from high enrichment fuel to low enrichment U-235 when operating materials testing reactors (MTRs). However, when operating an MTR reactor with low enrichment fuel, the fuel density has to be increased, which is advantageously possible by using uranium fuel in oxides with a specific crystal size of 40 to 90 μm. It is. Conventionally, this type of fuel has been produced using industrially lossy and expensive methods.

Therefore, for example, West German Patent Publication No. 3024634
From the specification, U ₃ O ₈ powder with a crystal size of 40 to 90 μm can be produced by compression molding sinterable U ₃ O ₈ powder, sintering, crushing, and sieving the fine particles. Are known. The same process is then repeated again with the large particles remaining on the sieve. In this method, the yield of particles with a size of 40-90 μm is relatively low and the major proportion of U ₃ O ₈ powder occurs as unusable fine particles.

Moreover, during crushing, wear of the crusher occurs, which can be included as impurities in the U ₃ O ₈ powder and reduce its quality. Other disadvantages of this method include the dust generation caused during the crushing, which requires a correspondingly encapsulated process and leads to the formation of secondary waste in the exhaust gas purification system. Furthermore, it is known to start from an aqueous uranyl nitrate solution and add and mix tetrahydrofurfuryl alcohol thereto to produce a gel-like solution. This gel-like solution is diffused using a nozzle head that vibrates at a constant frequency. The spherical gel droplet ejected from the nozzle head flows through the descending section of the NH ₃ atmosphere, and then
It passes through a column filled with an aqueous NH ₃ solution, and at the bottom of the column it is collected as yellow particles containing uranium in the form of ammonium diuranate, so-called nuclides. The seeds are washed with an isopropanol/water mixture, then dried in vacuo and then calcined. Grain growth occurs in the subsequent sintering step. By sieving, the yield of crystals with a predetermined size of 40 to 90 μm is 70 to
Obtained at 80%. Fine and coarse particles must then be disposed of and worked up. Therefore, this method has a very large equipment loss and a large number of process steps. Furthermore, this process produces secondary waste in the form of an aqueous and isopropanol-containing ammonium nitrate solution.

Furthermore, U ₃ O ₈ powder is produced from a uranium compound with an oxidation number of +4 to +6 by ignition treatment in an oxygen-containing atmosphere, using air as the atmosphere and performing the ignition treatment at a temperature below 1100°C. is known. U ₃ O ₈ powders with a crystal size of 40 to 90 μm and, moreover, as non-porous as possible cannot be produced in this way.

The object of the invention is therefore to provide crystals that are economical, generate as little secondary waste as possible, and are as pore-free as possible. By igniting a finely powdered uranium compound with an oxidation number of +4 to +6 at normal pressure in an oxygen-containing atmosphere, crystals with a crystal size of 40 to 90 μm are produced.
The objective was to disclose a method for producing U ₃ O ₈ powder.

According to the present invention, this problem has been solved by igniting a uranium compound at a temperature of 1250° C. or higher in an atmosphere containing more than 30% by volume of oxygen.

In particular, the heat treatment is carried out at 1250-1550°C, preferably with oxygen.
It is carried out in an atmosphere containing 40-100% by volume. The use of pure oxygen proved to be most advantageous. Best results are obtained if the ignition treatment is maintained for 10 to 30 hours.

For example, uranium oxide of any oxidation number >2, which should have reactor purity but may optionally be in finely divided form, is placed on an aluminum oxide shear tray and placed in a Matsufuru reactor. This Matsufuru furnace is connected to an oxygen bottle, heated to 1500℃ in an oxygen stream, and heated to this temperature for about 10 to 10 minutes depending on the fineness of the raw material uranium oxide.
Leave for 30 hours.

The U ₃ O ₈ crystals produced in this way are non-porous, have a BET surface area <0.1 m ² /g and a toluene density of 8.32-8.34 g/cm ³ , while the theoretical density is
Since it is 8.39g/cm ³ , it is almost achieved.

In the method of the present invention, the yield of U ₃ O ₈ crystals with a ridge length of 40 to 90 μm is particularly high, exceeding 80%, and in most cases
Higher than 90%. Very large crystals and fine particles can be separated by sieving and further processed. A small amount of very large crystals can be added directly to the fuel product stream after being mechanically crushed to a size of 40 to 90 μm, and the fine particulate fraction can be fed directly back into the manufacturing process, so that the final result of this method is can be operated with almost quantitative yields without the formation of secondary wastes.

The process of the invention is particularly simple and economical, since it operates in one step and does not require large investments or consumption of chemicals, except for oxygen.

Instead of a pure oxygen atmosphere, the heat treatment can also be carried out in an atmosphere containing at least 30% by volume of oxygen together with an inert gas, but this requires a longer heat treatment, which makes this alternative It is uneconomical because the time loss is greater than in the atmosphere.

In producing U ₃ O ₈ crystals by the method of the present invention,
It is particularly surprising that uranium oxide with arbitrarily small raw material crystal sizes and all uranium with an oxidation number of +4 to +6 can be used.

Using the U ₃ O ₈ powder thus produced, UO ₂ powder with the same crystal size of 40 to 90 μm can also be produced. For this purpose, U ₃ O ₈ with a particle size of 40-90 μm is used.
The crystals are deposited on a molybdenum Schare and in a continuous extrusion furnace (Durchstopofen), especially in a hydrogen atmosphere.
Heat treatment at 850-1700°C for about 8-20 hours.

This treatment method yields UO ₂ crystals whose appearance is identical to U ₃ O ₈ crystals and which are likewise non-porous.

Claims (1)

[Claims] 1. A method for producing U ₃ O ₈ powder with a crystal size of 40 to 90 μm by igniting a finely powdered uranium compound having an oxidation number of +4 to +6 at normal pressure in an oxygen-containing atmosphere, 30 at temperatures above 1250℃
A method for producing U ₃ O ₈ powder, characterized by ignition treatment in an atmosphere containing oxygen in an amount greater than % by volume. 2. The method according to claim 1, wherein the heat treatment is carried out at 1250 to 1550°C. 3. The method according to claim 1 or 2, wherein the heat treatment is performed in pure oxygen. 4. The method according to any one of claims 1 to 3, wherein the heat treatment is performed for 10 to 30 hours.